This invention relates to solid pharmaceutical compositions comprising a stable salt of quinapril, specifically the magnesium salt, quinapril magnesium.
Some ACE (Angiotensin Converting Enzyme) inhibitors, which are useful as antihypertensives, are susceptible to degradation by cyclization, hydrolysis or oxidation. Such ACE inhibitors include enalapril, quinapril and moexipril, and acid addition salts thereof.
Enalapril and its acid addition salts and their use as ACE inhibitors, is disclosed in U.S. Pat. No. 4,374,829.
Quinapril and moexipril and their acid addition salts are disclosed in U.S. Pat. No. 4,344,949.
Various methods of improving the stability of these compounds are disclosed in the prior art.
Enalapril and its acid addition salts are more easily stabilized than quinapril and its acid addition salts. There are thus some methods in the prior art that are satisfactory for the stabilization of enalapril and its acid addition salts, but not quinapril and its acid addition salts.
U.S. Pat. No. 5,562,921 discloses that stable tablets can be made comprising enalapril maleate by restricting the inactive ingredients used in the tablets to certain ones found not to cause degradation. However, because quinapril and its acid addition salts are less stable than enalapril maleate, this approach does not work with quinapril and its acid addition salts.
U.S. Pat. No. 5,350,582 and U.S. Pat. No. 5,573,780 both disclose that stable tablets can be made by reacting enalapril maleate with an alkaline sodium compound to convert the enalapril maleate to enalapril sodium. Enalapril sodium is found to be much more stable than enalapril maleate.
U.S. Pat. No. 4,830,853 discloses that certain ACE inhibitors, and in particular quinapril, can be stabilized against oxidation and discoloration by including ascorbic acid or sodium ascorbate in the composition. However, it appears that this approach does not stabilize quinapril or its addition salts sufficiently to be commercially useful, as products presently being marketed do not use this approach.
Finally, U.S. Pat. No. 4,743,450 discloses that certain ACE inhibitors, and in particular, quinapril and its acid addition salts can be stabilized by making solid compositions that include an alkaline compound as stabilizer. Magnesium, calcium and sodium compounds are said to be preferred, and magnesium is most preferred. The examples in this patent all relate to solid dosage forms comprising quinapril hydrochloride as active drug and magnesium carbonate as stabilizer.
There is also a publication by Gu et al, xe2x80x9cDrug-Excipient Incompatibility Studies of the Dipeptide Angiotensin Converting Enzyme Inhibitor, Moexipril Hydrochloride: Dry Powder vs Wet Granulationxe2x80x9d, Pharm Res.7(4):370-383. This publication discloses that moexipril hydrochloride can be stabilized by making compositions comprising moexipril hydrochloride and an alkaline stabilizing agent selected from sodium bicarbonate, sodium carbonate and calcium carbonate. It is stated that the stabilization is accomplished only when the compositions are made by a wet granulation process. In the conclusion of the publication, it is postulated that the stabilization results from the neutralization of the acidic drug by the basic excipient at the outer surface of the granulated material. It is also stated that it is possible that a portion of the moexipril was converted to alkaline salts via granulation. It thus appears clear that Gu et at teaches that only a portion (if any) of the drug, and only that portion at the outer surface of the granules, may be converted to the alkaline salt, and that the stable product thus results entirely or primarily not from conversion to alkaline salts, but from stabilization of the moexipril hydrochloride by the presence of the alkaline stabilizing compound in the final product.
Gu et al is thus consistent with the teaching of U.S. Pat. No. 4,743,450, which, as aforesaid, teaches stable compositions comprising the unstable drug, stabilized by the presence of an alkaline compound in the final composition.
Tablets containing quinapril hydrochloride are sold in the United States and elsewhere under the tradename Accupril(copyright) by Warner-Lambert Company. The labeling of these tablets indicates that the tablets contain quinapril hydrochloride and magnesium carbonate. This indicates that these tablets are compositions in accordance with the teaching of U.S. Pat. No. 4,743,450.
There are certain problems inherent in the teaching of U.S. Pat. No. 4,743,450. In particular:
1. The examples of U.S. Pat. No. 4,743,450 indicate a ratio of magnesium carbonate to quinapril hydrochloride from about 5.8 to about 16.5 by weight, so that it appears that the amount of magnesium compound required is large and substantially exceeds the amount of the quinapril hydrochloride.
2. Using the approach of U.S. Pat. No. 4,743,450, it is difficult to precisely control the exact final ingredients in the composition. The quinapril hydrochloride and magnesium carbonate are capable of an acid-base reaction. It is difficult to control the process so as to completely avoid an acid-base reaction in the making of the composition. The exact composition of the final product is thus uncertain and probably variable, if the teaching of U.S. Pat. No. 4,743,450 is followed.
In light of the prior art, the object of the present invention is to enable a stable composition comprising a quinapril salt which overcomes these limitations of the prior art.
It has been found that the magnesium salt of quinapril (i.e. quinapril magnesium) is sufficiently stable to enable stable solid compositions, without the presence of an alkaline stabilizing compound in the final composition.
It has also been found that stable solid compositions comprising quinapril magnesium can be made using quinapril or an acid addition salt thereof, by reacting the quinapril or acid addition salt with an alkaline magnesium compound, so as to convert all or substantially all of the quinapril or acid addition salt to quinapril magnesium.
Since the purpose of the present invention is to eliminate the unstable quinapril or acid addition salt thereof and replace it with stable quinapril magnesium, it will be understood that xe2x80x9call or substantially allxe2x80x9d in the preceding paragraph means that the remaining quantity of quinapril or acid addition salt thereof, if any, will be small enough that any degradation thereof will not be significant to the stability of the final product. Hence xe2x80x9call or substantially allxe2x80x9d will be understood to mean that at least about 80% of the quinapril or addition salt thereof is converted to quinapril magnesium, preferably at least 90%, more preferably at least 95%, and most preferably 100% or virtually 100%.
The quinapril or acid addition salt thereof used in the process will preferably be quinapril hydrochloride.
The alkaline magnesium compound will preferably be magnesium hydroxide or the magnesium salt of a weak acid such as, for example, magnesium carbonate. Magnesium oxide may be used in place of magnesium hydroxide, as magnesium oxide will convert to magnesium hydroxide in the presence of water.
The molecular formula for quinapril hydrochloride is C25H30N2O5.HCl and the molecular weight is 475.0g.
The molecular equations, for converting quinapril hydrochloride to quinapril magnesium plus magnesium chloride, by reacting with magnesium hydroxide and magnesium carbonate are as follows:
1) Using magnesium hydroxide:
2C25H30N2O5.HCl+2Mg(OH)2xe2x86x92Mg(C25H29N2O5)2+MgCl2+4H2O
2) Using magnesium carbonate:
2C25H30N2O5.HCl+2MgCO3xe2x86x92Mg(C25H29N2O5)2+MgCl2+2H2O+2CO2 
It can be seen that a complete conversion of quinapril hydrochloride to quinapril magnesium plus magnesium chloride requires for each mole (475g) of quinapril hydrochloride, the following minimum amount of alkaline magnesium compound:
i) If magnesium hydroxide is used, one mole, which is 58.3g.
ii) If magnesium carbonate is used, one mole, which is 84.3g.
If only the minimum amount of alkaline magnesium compound, so calculated, is used, it is possible that the reaction may not go to completion, leaving some of the quinapril or acid addition salt not converted to quinapril magnesium. It is thus preferable to use an excess amount of alkaline magnesium compound, to help ensure the reaction is complete or substantially complete.
A reaction to convert the quinapril or acid addition salt thereof to quinapril magnesium cannot be accomplished simply by mixing the quinapril or acid addition salt together with the alkaline magnesium compound in dry for. It is thus necessary to mix and react the quinapril or acid addition salt and the alkaline magnesium compound with the aid of solvent, which may be water or organic solvent or a mixture of water and organic solvent, and then evaporating the solvent to obtain a dry substance. The solvent will preferably be a mixture of water and organic solvent, and a preferred organic solvent is acetone. After the solvent is evaporated, the dried material obtained will be further processed into a dosage form, such as a tablet or capsule. This process may be carried out in any of several ways, as follows:
i) The quinapril or acid addition salt and the alkaline magnesium compound can be reacted by adding them to solvent and mixing in the liquid state until the reaction is complete. As aforesaid, the solvent may be water or organic solvent, or a mixture of water and one or more organic solvents. The solvent will preferably be a mixture of water and an organic solvent, and most preferably a mixture of water and acetone. The amount of solvent will preferably be sufficient to fully dissolve the resultant quinapril magnesium, but not necessarily the excess alkaline magnesium compound, assuming an excess was used. After the reaction is completed, it is necessary to evaporate the solvent. This can be done, for example, by filtering the liquid to remove the extra alkaline magnesium compound, if any, and then spray drying. The resulting dry powder will be a mixture of quinapril magnesium and the magnesium salt of the acid used in the quinapril acid addition salt (i.e. magnesium chloride if quinapril hydrochloride was used). This dry powder can then be mixed with other suitable excipients (i.e. inactive ingredients such as, for example, lactose), and that mixture can be further processed into solid compositions; i.e. compressed into tablets or used as fill for two-piece hard gelatin capsules.
i) The quinapril or acid addition salt and the alkaline magnesium compound can be reacted in a liquid state as described in i) above. However, instead of then evaporating the solvent, the restraint liquid or suspension can be used to wet granulate other excipients, and the wet mass can then be dried, for example, in a oven or fluid bed drier. The dried mass can then be compressed into tablets or used as fill for capsules, with or without the addition of other excipients.
iii) The quinapril or acid addition salt can be mixed with one or more excipients, for example lactose, in a dry state. and then the dry mixture can be wet granulated with a solution or suspension of the alkaline magnesium compound in suitable solvent, thereby forming a wet mass. A sufficient quantity of suitable solvent must be used and the mass must be left wet enough for sufficient time to enable the reaction between the quinapril or acid addition salt and the alkaline magnesium compound to be complete or substantially complete, before the solvent is removed by drying the wet mass. The wet mass is then dried, and the dried material can then be compressed into tablets or used as a fill for capsules, with or without the addition of other excipients.
iv) The magnesium compound can be mixed with other excipients, for example lactose, in a dry state, and then the dry mixture can be wet granulated with a solution or suspension of the quinapril or acid addition salt in suitable solvent, thereby forming a wet mass. Again, a sufficient quantity of suitable solvent must be used and the mass must be left wet enough for sufficient time to enable the reaction between the quinapril or acid addition salt and the alkaline magnesium compound to be complete or substantially complete, before the solvent is removed by drying the wet mass. The wet mass is then dried, and the dried material can then be compressed into tablets or used as a fill for capsules, with or without the addition of other excipients.
v) The quinapril or acid addition salt thereof and the alkaline magnesium compound can both be mixed with other excipients, for example lactose, in a dry state and then the dry mixture can be wet granulated with solvent to form a wet mass. Again, a sufficient quantity of suitable solvent must be used and the mass must be left wet enough for sufficient time to enable the reaction between the quinapril or acid addition salt and the alkaline magnesium compound to be complete or
vi) substantially complete, before the solvent is removed by drying. The wet mass is then dried, and the dried material can then be compressed into tablets or used as a fill for capsules, with or without the addition of other excipients.
The invention will be further understood from the following examples which are intended to be illustrative but not limiting of the invention.